1. Field of the Invention
The present invention is directed to a formaldehyde-free method for treating substrates, especially wood products, such as lumber, to strengthen the substrate and to render it flame-retardant and resistant to moisture and insects.
2. Description of Related Art
Over the years, much effort has been directed to solving the problem of imparting fire-inhibiting properties to wood, as well as resistance to the growth of fungi, attack by termites, and moisture. Initial efforts aimed at imparting fire-inhibiting properties to wood included impregnation of the wood with fire-inhibiting salts that are applied in aqueous solution. For example, ammonium sulfate, sodium sulfate or magnesium sulfate, mono ammonium phosphate or diammonium phosphate, borates, or the like have been used. The fire-inhibiting or flameproofing effect of such salts may be based on the fact that their decomposition is endothermic and that on being heated, they easily form salts which envelop the inflammable substance, so that combustible gases are not given off and the wood carbonizes without any flames being formed. The use of such salts has a shortcoming, however, as even though they could easily impregnate the wood, they were rather easily washed out of the wood again due to their excellent water solubility.
U.S. Pat. No. 3,935,341 to Sorensen et al. discloses another method of imparting fire and pest resistance to wood. This method renders wood fire-resistant by impregnating the wood with a solution of phenol and a fire-inhibiting salt, drying the wood, followed by treating the wood with a solution of formaldehyde, which is polymerizable with the phenol. Heating the treated wood to dryness causes polymerization of the monomers. Wood products, such as those disclosed by Sorensen et al., have fallen out of favor in recent years due to the potential toxic environmental effects of residual formaldehyde in the treated wood.
U.S. Pat. Nos. 3,945,835 and 4,038,086 to Clarke et al. and U.S. Pat. No. 4,103,000 to Hartford disclose various aqueous wood treating and/or preservative compositions that contain copper ammonium and/or zinc ammonium cations and arsenic or arsenious anions to make, for example, chromated copper arsenate wood treating compositions. While effective at preserving wood, these materials are able to be leached from the wood by water and owing to the toxic nature of the compositions, can create a potential to harm the environment.
The most common wood preservative used in the United States is chromated copper arsenate (CCA). CCA is composed of the oxides of chromium, copper, and arsenic. The copper in the wood serves as a fungicide while the arsenic protects the wood from insects. A particular problem is encountered when CCA treated lumber is disposed of.
Typically, CCA treated lumber ends up in unlined landfills when disposed. However, there are growing concerns about the environmental impact of CCA treated lumber because surface and ground water eventually leach the various metals from the wood. CCA treated lumber has been identified as a major potential cause of elevated arsenic and chromium concentrations in the environment.
U.S. Pat. No. 3,974,318 to Lilla discloses a process whereby water soluble silicate compositions are applied to a wood product, and the product is subsequently treated with a water soluble metallic salt compound to form a water insoluble metallic silicate in the wood product. Improvements on this method have been disclosed in U.S. Pat. No. 6,235,349 to Grantham et al., U.S. Pat. No. 5,478,598 to Shiozawa, and U.S. Pat. Nos. 6,146,766 and 6,040,057 to Slimak et al. However, in all of these cases, the silicate-based treatment compositions can be leached from the wood by exposure to environmental water and moisture, which eventually causes the treated wood to loose its fire, insect, termite, and microbial attack resistance.
The use of boron-based formulation for wood preservation has been investigated because of the low acute oral and dermal toxicity of these materials, as well as their ability to render wood non-flammable when applied. Zinc borate hydrate, boric oxide, boric acid, borax, and disodium octaborate tetrahydrate (DOT) have become popular compounds for treating wood because of their ability to render wood resistant to decay from fungi, wood boring beetles, termites, and general household pests, such as cockroaches and silverfish. The use of boron-based treatments are generally limited to indoor use, as they are easily leached from the treated wood by environmental water and moisture.
There is an ongoing need for an environmentally safe composition and method for treating wood to render fire-inhibiting properties, as well as resistance to the growth of fungi, attack by termites, and moisture, especially lumber, wherein the treatment composition is resistant to being removed or leached from the treated wood due to exposure to environmental water and moisture.
The present invention is directed to a method of treating substrates, such as wood. The method includes the steps of (1) applying an alkali silicate solution to one or more substrates and (2) applying an alkali borate solution with boric oxide (B2O3) content to the substrates. The present invention is also directed to substrates that have been treated using the present method. Further, the present invention is directed to treated substrates that include a borate-silicate polymer within the substrate. Moreover, the present invention is directed to structures built using wood treated using the present method.